Abstract
Summary: Seven distinctive thin clay beds and beds of clay with pyrite are described from the Arnsbergian of Staffordshire, Derbyshire and Cheshire. Correlations using these beds are made between the north Staffordshire basin area, Edale, and the Ashover boreholes. The beds are identified mineralogically as K-bentonites consisting of mixed layer, randomly interstratified mica-montmorillonite with variable amounts of kaolinite. The mica polymorph is dioctahedral and is identified as the 1 Md structure of low temperature origin. K-bentonites contrast markedly with the detrital shales above and below them, which contain quartz, chlorite and detrital mica probably of 2M high temperature structure. The K-bentonites are considered to be beds of altered wind-blown ash. Within north Staffordshire and Derbyshire they provide a means of correlation independent of the goniatite horizons.

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